At least five people have been killed in the US as dozens of tornadoes tore through parts of Oklahoma, Kansas, Nebraska and Iowa.
The five people died in Oklahoma after storm sirens failed to sound in one town and people were caught unaware.
Woodward Mayor Roscoe Hill said lightning apparently disabled the town's storm warning system.
Mr Hill said: "This thing took us by surprise. It's kind of overwhelming."
He said he was told the tornado hit the west and north sides of the town, badly damaging an apartment complex.
The storms happened across what is often called "Tornado Alley" in the central and southern plains and more are forecast for later today.
The National Weather Service said the worst conditions were expected in Oklahoma, Nebraska and Kansas, while other areas could see baseball-sized hail and strong winds.
